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Fatty acids

A fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated.

Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28.

Fatty acids are usually derived from triglycerides or phospholipids.

Important sources of fuel because, when metabolized, they yield large quantities of ATP.

Many cell types can use either glucose or fatty acids for this purpose.

Long-chain fatty acids cannot cross the blood-brain barrier and cannot be used as fuel by the cells of the central nervous system.

Free short-chain fatty acids and medium-chain fatty acids can cross the blood-brain barrier, in addition to glucose and ketone bodies.

Fatty acids that have carbon-carbon double bonds are known as unsaturated.

Consumption of unsaturated fatty acids has been found to decrease LDL cholesterol levels and increase HDL cholesterol levels in the blood, thus reducing the risk of contracting cardiovascular diseases.

No lower safe limit of specific saturated fatty acid intakes has been identified.

There are two types of unsaturated oils: mono- and poly-unsaturated fats, both of which are recognized as beneficial to health in contrast to saturated fats.

 

Some vegetable oils, such as canola, sunflower, safflower, and olive oils contain high amounts of unsaturated fats.

 

Fatty acids without double bonds are known as saturated.

Saturate and unsaturated fatty acids differ in length.

Fatty acid chains differ by length, often categorized as short to very long.

Fatty acids derived from fish oil are long chain omega-3 polyunsaturated fatty acids: eicosapentaenoic and docosahexaenoic.

Short-chain fatty acids (SCFA) are fatty acids with aliphatic tails of fewer than six carbons.

Medium-chain fatty acids (MCFA) are fatty acids with aliphatic tails of 6�12 carbons, which can form medium-chain triglycerides.

Long-chain fatty acids (LCFA) are fatty acids with aliphatic tails 13 to 21 carbons.

Very long chain fatty acids (VLCFA) are fatty acids with aliphatic tails longer than 22 carbons.

Unsaturated fatty acids have one or more double bonds between carbon atoms.

Pairs of carbon atoms connected by double bonds can be saturated by adding hydrogen atoms to them, converting the double bonds to single bonds.

Double bonds are called unsaturated.

The two carbon atoms in the chain that are bound next to either side of the double bond can occur in a cis or trans configuration.

The more double bonds the chain has in the cis configuration, the less flexibility it has.

Most fatty acids in the trans configuration are not found in nature and are the result of processing by hydrogenation.

The differences in geometry between the types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes.

Fatty acids that are required but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids.

There are two series of essential fatty acids: one has a double bond three carbon atoms removed from the methyl end; the other has a double bond six carbon atoms removed from the methyl end.

Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).

Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side.

Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA), which are widely distributed in plant oils.

The human body has a limited ability to convert alpha-linolenic acid (ALA), into the longer-chain omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish.

Saturated fatty acids have no double bonds.

Thus, saturated fatty acids are saturated with hydrogen, as double bonds reduce the number of hydrogens on each carbon

Arachidic acid, is a saturated fatty acid.

Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids.

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Fatty acids circulating in the plasma not in their glycerol ester form (glycerides), they are known as non-esterified fatty acids (NEFAs) or free fatty acids (FFAs).

Free fatty acids (FFAs) is a misnomer because they are transported complexed with a transport protein, such as albumin.

The term free fatty acids (FFAs) conveys the idea that they are circulating and available for metabolism.

Fatty acids can exist in various states of saturation.

Unsaturated fatty acids include monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs).

Conjugated fatty acids are a subset of PUFAs.

Fatty acids are usually produced industrially by the hydrolysis of triglycerides, and the removal of glycerol.

Some fatty acids are produced synthetically by hydrocarboxylation of alkenes.

Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids.

Almost all natural fatty acids, have even numbers of carbon atoms.

When synthesis is complete the free fatty acids are nearly always combined with glycerol to form triglycerides.

There are three fatty acids to one glycerol molecule in triglycerides, the main storage form of fatty acids.

FAs are important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed.

Phospholipids form the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus.

Free fatty acids found in the circulation come from the breakdown of stored triglycerides.

FFAs are insoluble in water, and are transported bound to plasma albumin.

FFA levels in the blood are limited by the availability of albumin binding sites.

They can be taken up by all cells that have mitochondria, except for those of the CNS.

Fatty acids can only be broken down to CO2 and water in mitochondria.

Cells in the central nervous system cannot take free fatty acids up from the blood, as the blood-brain barrier is impervious to free fatty acids.

Central nervous system cells have to manufacture their own fatty acids from carbohydrates, in order to produce and maintain the phospholipids of their cell membranes, and those of their organelles

The following table gives the fatty acid, vitamin E and cholesterol composition of some common dietary fats.

Saturated Monounsaturated Polyunsaturated Cholesterol Vitamin E

g/100g g/100g g/100g mg/100g mg/100g

Lard 40.8, 43.8, 9.6, 93, 0.60

Duck fat 33.2, 49.3, 12.9, 100 2.70

Butter 54.0 19.8 2.6 23.0 2.00

Vegetable fats

Coconut oil 85.2 6.6 1.7 0 .66

Cocoa butter 60.0 32.9 3.0 0 1.8

Palm kernel oil 81.5 11.4 1.6 0 3.80

Palm oil 45.3 41.6 8.3 0 33.12

Cottonseed oil 25.5 21.3 48.1 0 42.77

Wheat germ oil 18.8 15.9 60.7 0 136.65

Soybean oil 14.5 23.2 56.5 0 16.29

Olive oil 14.0 69.7 11.2 0 5.10

Corn oil 12.7 24.7 57.8 0 17.24

Sunflower oil 11.9 20.2 63.0 0 49.00

Safflower oil 10.2 12.6 72.1 0 40.68

Hemp oil 10 15 75 0 12.34

Canola/Rapeseed oil 5.3 64.3 24.8 0 22.21

Fatty acids undergo esterification and acid-base reactions.

As the chain length increases, the solubility of the fatty acids in water decreases very rapidly.

Unsaturated fatty acids undergo auto-oxidation, requiring oxygen and is accelerated by the presence of trace metals.

Vegetable oils resist this process because they contain antioxidants.

Fats and oils often are treated to remove the metal catalysts.

Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein.

Long-chain fatty acids are not directly released into the intestinal capillaries, but are absorbed into the fatty walls of the intestine villi and reassembled again into triglycerides.

The triglycerides are coated with cholesterol and protein into a chylomicron.

The chylomicron is released into a lymphatic capillary called a lacteal, which merges into larger lymphatic vessels.

It is transported via the lymphatic system and the thoracic duct up to a location near the heart

The thoracic duct empties the chylomicrons into the bloodstream via the left subclavian vein. At this point the chylomicrons can transport the triglycerides to tissues where they are stored or metabolized for energy.

Fatty acids,provided either by ingestion or by drawing on triglycerides stored in fatty tissues, are distributed to cells to serve as a fuel for muscular contraction and general metabolism.

They are broken down to CO2 and water by the intra-cellular mitochondria, releasing large amounts of energy, captured in the form of ATP through beta oxidation and the citric acid cycle.

Bloody fatty acids are taken in through the intestine in chylomicrons, but also exist in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) after processing in the liver.

In addition, when released from adipocytes, fatty acids exist in the blood as free fatty acids.

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